1. Field of the Invention
The present invention generally relates to method of resin sealing electronic parts, and more specifically, to a method of resin sealing an electronic part, the method having a step of resin sealing the semiconductor element and a bonding wire connected to an electrode such as an outside connection terminal of the semiconductor element.
2. Description of the Related Art
As today's electronic apparatuses have high function or high operability, it is required that the semiconductor devices applied to the electronic apparatuses also have high functionality or high operability.
Because of this, in a semiconductor element of the semiconductor device, especially in a large scale integrated circuit, plural functional circuits are received, and an active element such as a transistor forming the functional circuit block, a passive element such as resistance element, and a wiring are made minute and highly integrated.
Since the semiconductor element includes plural functional blocks, the semiconductor element requires a large number of outside connection terminals. Therefore, a gap or pitch between the outside connection terminals is further shortened. Because of this, a smaller diameter is applied to a bonding wire connecting to an outside connection terminal of the semiconductor element.
In addition, it is required that an electrode terminal on a supporting body such as the wiring board have a small size or high density. However, there is a limitation to making the electrode terminal have the small size or high density. Therefore, it may be difficult to provide the electrode terminal closer to the semiconductor element. Because of this, there is a tendency that the length of the bonding wire connecting the electrode terminal on the supporting body and the outside connection terminal of the semiconductor element is long.
Meanwhile, a resin sealing method as one of known sealing methods is applied when the semiconductor device is formed by sealing the semiconductor element and the bonding wire. As the resin sealing method, a transfer molding method has been conventionally used.
In the transfer molding method, the supporting body such as the wiring board or a lead frame, the semiconductor element mounted on the semiconductor element, a bonding wire connecting the outside connection terminal of the semiconductor element and the electrode terminal on the wiring board or the lead frame, and others are arranged in a mold. The sealing resin is pushed into the mold so that resin sealing is implemented. See Japanese Patent Application Publication No. 5-243301.
However, in such a transfer molding method, since the sealing resin is pushed into the mold at high pressure, the following problem may happen. That is, in a case where the diameter of the bonding wire is small or the length of the bonding wire is long, deformation and/or breaking of the bonding wire due to a flow of the sealing resin may happen and a short circuit with another bonding wire may be generated.
Because of this, instead of the transferring mold method, a compression molding method is disclosed.
In such a compression molding method, a resin sealed body, the resin sealed body including the supporting body such as the wiring board or a lead frame, the semiconductor element mounted on the semiconductor element, a bonding wire connecting the outside connection terminal of the semiconductor element and the electrode terminal on the wiring board or the lead frame, and others, is arranged in the upper mold. Powder or granular sealing resin is received in a cavity formed in the lower mold. The resin is heated so as to become molten. In this state, by closing the upper mold and lower mold, the resin sealed body is dipped in molten resin so that resin sealing is achieved.
According to such a compression molding method, since pushing the sealing resin into the mold is not implemented, there is little chance that the deformation and/or breaking of the bonding wire due to the flow of the sealing resin will happen.
Japanese Patent Application Publication No. 2002-137250 discloses a structure where a stick-shaped adjusting member is built in a metering part, to which metering part granules in a hopper are supplied in a such a way that the stick-shaped adjusting member can be freely squeezed into a metering hole, and the amount of the granules supplied is adjusted by controlling the amount of the adjusting member there is squeezed into the metering hole. Japanese Patent Application Publication No. 2004-216558 discloses a method whereby uniformly pressed granular resin is supplied to a mold cavity forming part almost simultaneously with sliding and opening of an on-off part in a resin supply mechanism in a horizontal direction so that the granular resin is uniformly pressed by pressure means at the time of opening the mold.
However, in the above-mentioned compression molding method, a flow of the sealing resin may be generated at the time when the sealing resin is molten due to the distribution of the sealing resin in the cavity formed in the lower mold. As a result of this, the deformation and/or breaking of the bonding wire due to the flow of the sealing resin may happen.
This problem is discussed below with reference to FIG. 1 through FIG. 7.
Here, FIG. 1 is a first view for explaining problems of a related art compression molding method. FIG. 2 is a second view for explaining problems of the related art compression molding method.
Referring to FIG. 1 and FIG. 2, a sealing resin receiving part 3 surrounded by a wall part 2 is provided in a substantially center of an upper surface of a sealing resin supply apparatus 1. In addition, bottom plates 4-1 and 4-2 are provided at a lower part of the sealing resin receiving part 3. The bottom plates 4-1 and 4-2 are opened and closed by being reciprocated in a horizontal direction.
A designated amount of powder or granular sealing resin is received in the entirety of the sealing resin receiving part 3 so that the thickness of the sealing resin in the sealing resin receiving part 3 is substantially uniform. Such a sealing resin supply apparatus 1 is provided above a lower mold 7 as shown in FIG. 3.
As shown in FIG. 3, a cavity forming part 10 is formed in a center part of an upper surface of the lower mold 7. The cavity forming part 10 is surrounded by a frame part 8 elastically supported by a spring 11. A release film 9 covers a bottom surface of the cavity forming part 10 and a surface of the frame part 8.
The bottom plate 4-1 provided at the sealing resin receiving part 3 is slid in a left direction and the bottom plate 4-2 provided at the sealing resin receiving part 3 is slid in a right direction as shown by arrows S1 in FIG. 3, so that the sealing resin 5 received in the sealing resin receiving part 3 falls into the cavity forming part 10 of the lower mold 7. The lower mold 7 is heated at, for example 175° C. Because of this, the sealing resin 5 received in the cavity forming part 10 is melted.
According to the method of supplying the sealing resin 5 to the mold, since the bottom surface of the sealing resin receiving part 3 is opened by sliding the bottom plates 4-1 and 4-2, as shown in FIG. 4, the sealing resin 5 that has fallen down into the cavity forming part 10 of the lower mold 7 is piled up and the piled amount of the resin 5 near the area of the frame part 8 in the cavity forming part 10 is large so that the distribution of the sealing resin 5 in the cavity forming part 10 may be non-uniform.
After the sealing resin 5 is supplied into the cavity forming part 10 of the lower mold 7, the sealing resin supply apparatus 1 is removed from the upper part of the lower mold 7. The lower mold 7 immediately moves (is raised) in a direction shown by an arrow S2 so that the lower mold 7 and the upper mold 15 are mold closed.
In the upper mold 15, a body to be resin sealed is held by a clamp part 16 and vacuum suction via a vacuum suction hole 17. Here, the body has a structure where plural semiconductor elements 22 are mounted on and fixed to a main surface of a single wiring board 21 and an outside connection terminal of the semiconductor element 22 and an electrode terminal on the wiring board 21 are connected by the bonding wire 23. The wiring board 21 is arranged and held at the upper mold 15.
At the time of mold closing, the sealing resin 5 may flow from the vicinity of the frame part 8 to the center part in the cavity 10 of the lower mold 7, as shown by arrows S3 in FIG. 5. Because of this, if the semiconductor element 22, the bonding wire 23, and others held by the upper mold 15 are dipped into the sealing resin 5, the deformation and/or breaking of the bonding wire due to the flow of the sealing resin 5 may happen.
In FIG. 5, for explanation of the flow of the sealing resin 5, a state where the upper mold 15 and the lower mold 7 are separated is shown.
In addition, after the sealing resin 5 is distributed in the cavity forming part 10 so that the thickness of the sealing resin 5 is uniform, when the lower mold 7 moves in a direction shown by an arrow S2 in FIG. 6 for mold closing of the upper mold 15 and the lower mold 7, and the resin sealed body held by the upper mold 15 is dipped in the sealing resin 5, a flow of the sealing resin 5 in directions shown by arrows S4 in FIG. 6 may be generated due to an action of the semiconductor element 22 pushing and dividing the sealing resin 5.
Due to such a flow of the sealing resin 5, the deformation and/or breaking of the bonding wire 23 may happen.
In the resin sealed body, as shown in FIG. 7, the semiconductor element 22 may not be mounted on a part of the wiring board 21.
As a result of this, in a case where an arrangement of the semiconductor element 22 in the cavity forming part 10 is not uniform, as shown by arrows S5, a flow of the sealing resin 5 to a space where a semiconductor element 22 is not arranged may be generated. In such a case, the deformation and/or breaking of the bonding wire 23 may happen.